Charge Cloud Research Articles

Estimation of Charge Transfer During Long Continuing Currents in Natural Downward Flashes Using Single‐Station E‐Field Measurements

AbstractThe amount of charge transferred to ground during long continuing currents in natural downward flashes can be obtained either through direct current measurements or using remote electromagnetic fields, if direct measurements are not feasible. In this study, measurements of a single‐station E‐field antenna were used to estimate charge transfer during continuing currents. With time‐synchronized high‐speed video recordings serving as ground‐truth data for continuing current occurrence, we estimate transferred charge during long continuing currents in 140 natural downward flashes from electric field changes, assuming a simple monopole charge model. We present average parameters for the duration, transferred charge, amplitude, and the average amplitude on five segments along the channel. Further, we perform a simulation to investigate the estimation performance of the monopole charge model, when the cloud charge is spatially extended. Using an extended charge distribution model, we generate single‐station remote field waveforms and infer the charge with the monopole model. Comparison of the known and inferred charge yields estimation errors depending on the leader orientation, its spatial extension, and the observation distance. A Monte Carlo approach is carried out to statistically evaluate parameter deviations. This novel estimation error analysis sheds light on the limitations of the applied simple techniques for charge transfer estimation of long continuing currents using single‐station electric field measurements.

Characteristics of Negative Lightning Return Strokes in a Tropical and Non-Tropical Region—A Comparative Perspective

Lightning is a naturally occurring phenomenon that involves a sudden electrostatic discharge caused by an imbalance between electrically charged cloud regions. Although lightning is visibly amazing, its impact can be dangerous and damaging, which many studies have carried out lightning-generated electric field measurements to assess the electrical discharge features. This study conducted the lightning-generated electric field measurement on the College of Engineering building rooftop at UNITEN from August 2019 to March 2020. A total of 115 negative lightning return strokes waveforms were recorded using a parallel plate antenna. A comparison was made between the data measured in the tropical and non-tropical regions, such as UTM, UPM, Sweden, USA, and Germany, in terms of the characteristic, mainly on the negative return strokes parameters. It was observed that data measured in the same region, either tropical or non-tropical, were consistent or almost similar. On the contrary, the results indicated a significant difference between these two regions on the negative return strokes parameters characteristics. The zero-to-peak and fast transition 10–90% rise time, as well as width dE/dt pulse at half peak value in the tropical region, were observed higher than the non-tropical region. Meanwhile, the zero-crossing time and slow front amplitude relative to the peak in the non-tropical region were averagely longer as compared to the tropical region. Therefore, dissimilarities in the characteristics of negative return stroke parameters could be attributed to the variation in the meteorological conditions, geographical locations, and climatic affection.

A New Electric Field Mill Network to Estimate Temporal Variation of Simplified Charge Model in an Isolated Thundercloud.

The gross charge distribution in an electrified cloud has already been estimated by polarity distribution of the electrostatic field on the ground surface. While either a dipole or a tripole charge structure is commonly accepted, the increase–decrease and motion of each point charge in those models are both still unclear. This paper presents a new network of electric field mills for multipoint electrostatic measurement to evaluate the temporal variations of a simple cloud charge model with second-scale resolution. Details of our newly developed equipment are described, with an emphasis on its advantages. This network was deployed in the north Kanto area of Japan and operated during the summer season in 2020. In order to simplify the relationship between cloud charge positions and the horizontal distribution of the measured electrostatic field, an isolated thundercloud is focused on. As an initial analysis, a negative point charge model is applied to an isolated cloud observed on 27 August 2020. The quantity and height of the point charge were estimated as being approximately −20 C and 7 km, respectively. The calculated charge location is generally coincident with the C-band radar echo regions. Significant correspondence is demonstrated between the intensity distribution of the electrostatic fields measured at seven sites and that calculated with estimated point charge. This result indicates the possibility to determine the amounts and positions of cloud charges inside the dipole charge structure based on multipoint measurement of the electrostatic field.

Effective description of non-equilibrium currents in cold magnetized plasma

The dynamics of cold strongly magnetized plasma -- traditionally the domain of force-free electrodynamics -- has recently been reformulated in terms of symmetries and effective field theory, where the degrees of freedom are the momentum and magnetic flux carried by a fluid of cold strings. In physical applications where the electron mass can be neglected one might expect the presence of extra light charged modes -- electrons in the lowest Landau level -- propagating parallel to the magnetic field lines. We construct an effective description of such electric charges, describing their interaction with plasma degrees of freedom in terms of a new collective mode that can be thought of as a bosonization of the electric charge density along each field line. In this framework QED phenomena such as charged pair production and the axial anomaly are described at the classical level. Formally, our construction corresponds to gauging a particular part of the higher form symmetry associated with magnetic flux conservation. We study some simple applications of our effective theory, showing that the scattering of magnetosonic modes generically creates particles and that the rotating Michel monopole is now surrounded by a cloud of electric charge.

An analytical model for dust impact voltage signals and its application to STEREO/WAVES data

Context. Dust impacts have been observed using radio and wave instruments onboard spacecraft since the 1980s. Voltage waveforms show typical impulsive signals generated by dust grains. Aims. We aim at developing models of how signals are generated to be able to link observed electric signals to the physical properties of the impacting dust. To validate the model, we use the Time Domain Sampler (TDS) subsystem of the STEREO/WAVES instrument which generates high-cadence time series of voltage pulses for each monopole. Methods. We propose a new model that takes impact-ionization-charge collection and electrostatic-influence effects into account. It is an analytical expression for the pulse and allows us to measure the of amount of the total ion charge, Q, the fraction of escaping charge, ϵ, the rise timescale, τi, and the relaxation timescale, τsc. The model is simple and convenient for massive data fitting. To check our model’s accuracy, we collected all the dust events detected by STEREO/WAVES/TDS simultaneously on all three monopoles at 1AU since the beginning of the STEREO mission in 2007. Results. Our study confirms that the rise time largely exceeds the spacecraft’s short timescale of electron collection. Our estimated rise time value allows us to determine the propagation speed of the ion cloud, which is the first time that this information has been derived from space data. Our model also makes it possible to determine properties associated with the electron dynamics, in particular the order of magnitude of the electron escape current. The obtained value gives us an estimate of the cloud’s electron temperature – a result that, as far as we know, has never been obtained before except in laboratory experiments. Furthermore, a strong correlation between the total cloud charge and the escaping charge allows us to estimate the escaping current from the amplitude of the precursor, a result that could be interesting for the study of the pulses recently observed in the magnetic waveforms of Solar Orbiter or Parker Solar Probe, for which the electric waveform is saturated.

Pulse Compression Photoconductive Switching Using Negative Differential Mobility

This work demonstrates a novel optoelectronic device with the potential for use as a high-frequency, high-power RF source or amplifier. The device is a gallium–arsenide coplanar waveguide with a small gap in the signal trace for optical illumination. A confined charge cloud is generated by illumination through an aperture in an opaque mask over this gap. An electric field above the threshold for negative differential mobility (NDM) enables pulse compression, which prevents the charge cloud from spreading temporally during the drift process. Due to the NDM phenomenon, the output electrical pulse is temporally compressed compared to the input optical pulse. This phenomenon is demonstrated using three different experiments with varied laser pulsewidth (28–700 ps) and device geometry (50- and 100- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> -length gaps). A 66% reduction in the full-width at half-maximum of the electrical pulse relative to the input optical pulse was demonstrated. This novel coupled optoelectronic device opens avenues for high-frequency, high-power, compact devices that could enable next-generation satellite communication systems with faster data rates and longer ranges.

Measuring electrical properties of the lower troposphere using enhanced meteorological radiosondes

Abstract. In atmospheric science, measurements above the surface have long been obtained by carrying instrument packages, radiosondes, aloft using balloons. Whilst occasionally used for research, most radiosondes – around 1000 are released daily – only generate data for routine weather forecasting. If meteorological radiosondes are modified to carry additional sensors, of either mass-produced commercial heritage or designed for a specific scientific application, a wide range of new measurements becomes possible. A programme to develop add-on devices for standard radiosondes, which retains the core meteorological use, is described here. Combining diverse sensors on a single radiosonde helps interpretation of findings and yields economy of equipment, consumables and effort. A self-configuring system has been developed to allow different sensors to be easily combined, enhancing existing weather balloons and providing an emergency monitoring capability for airborne hazards. This research programme was originally pursued to investigate electrical properties of extensive layer clouds and has expanded to include a wide range of balloon-carried sensors for solar radiation, cloud, turbulence, volcanic ash, radioactivity and space weather. For the cloud charge application, multiple soundings in both hemispheres have established that charging at the boundaries of extensive layer clouds is widespread and likely to be a global phenomenon. This paper summarises the Christiaan Huygens medal lecture given at the 2021 European Geosciences Union meeting.

On the relationship between lightning superbolts and TLEs in Northern Europe

Lightning occurrence at higher latitudes in northwestern Europe is by far less frequent than mainland continental and the Mediterranean during most of the year. Yet, as recent studies suggest, this region harbors a large fraction of the most energetic lightning flashes on Earth, commonly referred to as superbolts. In this study, we examine the time/locations of intense cloud-to-ground (CG) strokes (>200 kA in absolute value), provided by Météorage for the 10.5-year period (from Jan 2010 to Jul 2020), to present a high-resolution map of their distribution, pointing out relevant discrepancies observed between -CG and + CG, respectively. We additionally investigate the potential of superbolts to result in short-lived optical phenomena above thunderstorms, collectively known as transient luminous events (TLEs). Observations in the region indicate that isolated superbolts with substantial charge moment change can produce sprites during low active marginal winter thunderstorms, in the absence of concurrent IC/CG activity several minutes before and after the event. An example is described when 3 sprites were captured in a similar context during the night of 7th/8th February 2016. We suggest that: i) convergence and aerosols advection from sea surface and busy shipping lanes may favour deep convection and cloud electrification on the English Channel with respect to surrounding areas. Inherent differences in cloud charge structure of sea based storms could lead to faster negative leader vertical velocity than those for storms over land, on average, and hence in larger peak currents, determining the winter peak of negative superbolts in the area; ii) areas occupied by the most populated superbolt clusters can be used to conduct future research in the region, aimed at better characterising microphysical properties of superbolts and their potential in generating TLEs.

Multiple Environmental Influences on the Lightning of Cold-Based Continental Convection. Part II: Sensitivity Tests for Its Charge Structure and Land–Ocean Contrast

Abstract In Part I, an electrification scheme was described and a simulation of an observed cold-based storm from the U.S. Great Plains was validated with electrical observations. Most charge in the storm was separated by rebounding collisions of secondary ice originating from prior graupel–snow collisions. In this Part II, sensitivity tests are performed with the control simulation (Part I) and influences from environmental factors (aerosols, temperature, moisture, and shear) on lightning are elucidated. Environmental factors [e.g., convective available potential energy (CAPE)] controlling updraft speed are salient. When ascent is reduced by 30% and 70%, flashes become 70% fewer and disappear, respectively; faster ascent promotes positive cloud-to-ground (+CGs) flashes. Since cloud base is too cold (1°C) for coalescence, cloud condensation nucleus aerosol concentrations do not influence the lightning appreciably. The electrical response to varying concentrations of active ice nuclei is limited by most ice particles being secondary and less sensitive—a natural “buffer.” Imposing a maritime sounding suggests that the land–sea contrast in lightning for such storms is due to the vertical structure of environmental temperature and humidity. Weak CAPE, and both entrainment and condensate weight from a low cloud base, suppress ascent and charging. Maritime thermodynamic conditions reduce simulated flash rates by two orders of magnitude. Reducing aerosol loadings from continental to maritime only slightly reinforces this suppression. Last, a conceptual model is provided for how any simulated storm is either normal because graupel/hail is mostly positively charged or else is inverted/anomalous because graupel/hail is mostly negatively charged, with environmental factors controlling the charging. Impacts from microphysical processes, including three processes of secondary ice production, on lightning are analyzed.

A Comparative Study of Straight-Strip and Zigzag-Interleaved Anode Patterns for MPGD Readouts

Due to their simplicity and versatility of design, straight strip or rectangular pad anode structures are frequently employed with micro-pattern gas detectors to reconstruct high precision space points for various tracking applications. The particle impact point is typically determined by interpolating the charge collected by several neighboring pads. However, to effectively extract the inherent positional information, the lateral spacing of the straight pads must be significantly smaller than the extent of the charge cloud. In contrast, highly interleaved anode patterns, such as zigzags, can adequately sample the charge with a pitch comparable to the size of the charge cloud or even larger. This has the considerable advantage of providing the same performance while requiring far fewer instrumented channels. Additionally, the geometric parameters defining such zigzag structures may be tuned to provide a uniform detector response without the need for so-called pad response functions, while simultaneously maintaining excellent position resolution. We have measured the position resolution of a variety of zigzag shaped anode patterns optimized for various MPGDs, including GEM, Micromegas, and micro-RWELL and compared this performance to the same detectors equipped with straight pads of varying pitch. We report on the performance results of each readout structure, evaluated under identical conditions in a test beam.

Charging and Levitation of Particles Using UV Irradiation and Electric Field

The charging and levitation of particles using UV irradiation in an upward electric field were investigated. Glass beads with a mass median diameter of 61 &#x03BC;m were used for the experiments. The particle layers formed on a glass plate were irradiated by UV light with wavelengths ranging from 240 to 400 nm. The particles in the top layer were positively charged by photoemission and levitated by the electrostatic forces. The fluxes and motions of the levitated particles were analyzed by digital processing of the images obtained with a high-speed camera. The charge of each levitated particle was determined by fitting the results calculated using the equation of motion to the experimentally obtained particle motion. The charge of the particles beginning to be levitated was determined by the force balance and thus was not affected by the UV irradiance. The positive charge of the levitated particles could be increased by continuous photoemission from the particles and decreased by the capture of photoelectrons emitted by other particles. Approximately 40&#x0025; of the levitated particles descended because of the negative charge clouds formed by the photoemission from the particle layers and the levitated particles. Furthermore, in a second set of experiments, an upward electric field was applied after UV irradiation. In these experiments, the particles in the top layer were levitated after applying the electric field. These particles could be gain more excess charges than the particles for which the levitation was governed by the force balance.

Influence of Charged Clouds on the Distribution of Atmospheric Electric Field with Altitude

Influence of Charged Clouds on the Distribution of Atmospheric Electric Field with Altitude

Application of lightning spatio-temporal localization method based on deep LSTM and interpolation

Lightning is a strong discharge phenomenon that occurs in nature and poses a great threat to people’s property and life safety. The generation of lightning originates from the continuous accumulation of electric charges in clouds, and the atmospheric electric field instrument, as a measurement device reflecting the most fundamental cause of lightning generation, is used to detect the occurrence of lightning, which has been very widely used due to its low price and easy installation. However, its detection results are directionless and the detection range is limited. Therefore, this paper proposed a method for spatio-temporal localization of lightning based on deep Long Short-Term Memory (LSTM) neural network and interpolation method. The time series data of electric field detected by 30 atmospheric electric field instruments was fed into deep LSTM network for training, and the prediction results were classified into five categories according to the time period of lightning occurrence by softmax function. Furthermore, data from the networked stations were interpolated using ordinary Kriging (OK) to obtain the electric potential distribution in Guangzhou city, which was used to infer the approximate area where lightning may occur. The above two algorithms passed the accuracy test respectively. Finally, two case studies were done based on LSTM-OK. The results show that it can obtain satisfactory prediction performance.

Triggered Negative Lightning‐Leaders That Propagated Into Thunderstorm Lower Positive Charge

AbstractWhen the electric field below a thunderstorm or other electrified cloud is around 10 kV/m, it is sometimes possible to initiate (“trigger”) an upward‐propagating lightning‐leader by launching a rocket that uncoils a wire from the ground. The triggered leader propagates upward from the tip of the wire lifted by the rocket. When the channel is hot enough, a flash is visible. Triggering is common when the leader carries positive charge, but not when it carries negative charge. This article is about four flashes consisting of triggered negative leaders that branched into low‐altitude regions of positive cloud charge over Langmuir Laboratory in central New Mexico. Measurements of current and the locations of leader channels are available for three of the four flashes. Some current pulses at the ground for Flash 2 originated at negative leader steps more than 3 km away, which is a greater distance than has been reported from video measurements. Flashes 3 and 4 propagated only into thunderstorm lower positive charge, and the average lightning‐charge densities inside the volumes occupied by these two flashes are remarkably close. Our best estimate of density for Flashes 3 and 4 lies between −4.2 and −1.8 C/km3, which is compatible with the large spread in cloud‐charge densities derived from instruments carried on airplanes or balloons into low positive regions in thunderstorms.

1-μm spatial resolution in silicon photon-counting CT detectors.

Purpose: Spatial resolution for current scintillator-based computed tomography (CT) detectors is limited by the pixel size of about 1mm. Direct conversion photon-counting detector prototypes with silicon- or cadmium-based detector materials have lately demonstrated spatial resolution equivalent to about 0.3mm. We propose a development of the deep silicon photon-counting detector which will enable a resolution of , a substantial improvement compared to the state of the art. Approach: With the deep silicon sensor, it is possible to integrate CMOS electronics and reduce the pixel size at the same time as significant on-sensor data processing capability is introduced. A Gaussian curve can then be fitted to the charge cloud created in each interaction.We evaluate the feasibility of measuring the charge cloud shape of Compton interactions for deep silicon to increase the spatial resolution. By combining a Monte Carlo photon simulation with a charge transport model, we study the charge cloud distributions and induced currents as functions of the interaction position. For a simulated deep silicon detector with a pixel size of , we present a method for estimating the interaction position. Results: Using estimations for electronic noise and a lowest threshold of 0.88keV, we obtain a spatial resolution equivalent to in the direction parallel to the silicon wafer and in the direction orthogonal to the wafer. Conclusions: We have presented a simulation study of a deep silicon detector with a pixel size of and a method to estimate the x-ray interaction position with ultra-high resolution. Higher spatial resolution can in general be important to detect smaller details in the image. The very high spatial resolution in one dimension could be a path to a practical implementation of phase contrast imaging in CT.

A Contrast Calibration Protocol for X-ray Speckle Visibility Spectroscopy

X-ray free electron lasers, with their ultrashort highly coherent pulses, opened up the opportunity of probing ultrafast nano- and atomic-scale dynamics in amorphous and disordered material systems via speckle visibility spectroscopy. However, the anticipated count rate in a typical experiment is usually low. Therefore, visibility needs to be extracted via photon statistics analysis, i.e., by estimating the probabilities of multiple photons per pixel events using pixelated detectors. Considering the realistic X-ray detector responses including charge cloud sharing between pixels, pixel readout noise, and gain non-uniformity, speckle visibility extraction relying on photon assignment algorithms are often computationally demanding and suffer from systematic errors. In this paper, we present a systematic study of the commonly-used algorithms by applying them to an experimental data set containing small-angle coherent scattering with visibility levels ranging from below 1% to ∼60%. We also propose a contrast calibration protocol and show that a computationally lightweight algorithm can be implemented for high-speed correlation evaluation.

Polarity Effect on Electric Tree Inception in HVDC Cable Insulation

This paper studies the influence of polarity of the applied voltage on DC tree inception in XLPE by analyzing dissipated and stored electric energies. Space charge dynamics, electric field distributions and resulting energies in the vicinity of the needle tip in the needle-plane type sample are calculated using the bipolar charge transport model. Simulations are performed for three modes of DC tree initiation: by applying continuous DC voltage, by grounding pre-stressed sample and by polarity reversal. In case of continuous DC, the estimated dissipated energy is found to be higher for positive applied voltage compared to negative that results in a lower inception voltage level. It is observed that the energy dissipation is controlled by the amount of mobile charge carriers and their mobility. In the case of trees due to grounding of pre-charged sample, differences in the electrostatic energy stored in the vicinity of the needle electrode right before grounding leads to tree inception at lower magnitude for the negative polarity compared to positive. Here, the amount of stored energy is dependent on the electric field controlled by the distribution of space charge in the material and the mobility of charge carriers plays a major role by defining locations of space charge clouds. When trees are initiated by polarity reversal, both stored energy before reversal and dissipated energy after, are in favor of tree inception during negative-to-positive transition than for the opposite. The obtained energy densities are compared with the threshold values required for tree inception by electromechanically induced cracks in the material. It is concluded that stored and/or dissipated energy are determining the polarity effect in DC tree inception.

Regular scalar charged clouds around a Reissner-Nordstrom black hole and no-hair theorems

In this work we reanalyze the possibility of finding bound states (scalar clouds) of a test, charged and complex-valued scalar field with mass and charge q in the background of a Reissner-Nordstrom black hole (RNBH). In order to determine the existence of such scalar clouds we impose suitable regularity conditions for the scalar field at the event horizon. We find numerical evidence for the absence of such clouds in the subextremal and extremal RNBH when the field is massive but not self-interacting. More importantly, we put forward a theorem that proves that such clouds cannot exist. On the other hand, when a suitable self-interacting potential is included, the theorem no longer applies, providing a heuristic justification behind the existence of charged clouds (Q-clouds) that were reported recently.

Inter-droplet force between magnetically polarizable Pickering oil-in-water nanoemulsions stabilized with γ-Al2O3 nanoparticles: Role of electrostatic and electric dipolar interactions

HypothesisThe presence of nanoparticles at oil-water interface influences the interaction forces between Pickering emulsions. When charged nanoparticles are at the oil-water interface of an electrostatically stabilized emulsion, in addition to the screened Coulombic interaction, electric dipolar force also influences the total inter-droplet force profiles. An in-depth understanding of the effects of such electric dipolar forces is essential for designing colloidally stable Pickering nanoemulsions for various applications. ExperimentsInter-droplet forces between γ-Al2O3 nanoparticle stabilized oil-in-water nanoemulsion, containing superparamagnetic nanoparticles (magnetically polarizable) in the oil phase, are measured using the magnetic-chaining technique at different pH and salt concentrations. The role of mono-, di- and tri-valent salts on the inter-droplet force profiles are assessed. FindingsForce measurement studies reveal a lowering of inter-droplet spacing, within the linear chains, for higher salt concentrations due to an increased screening. Strong interfacial attachment of the charged nanoparticles results in the formation of an asymmetric charge cloud leading to an electric dipolar interaction. Incorporating the contributions of electric dipolar and screened Coulombic interactions, the theoretically estimated total repulsive force magnitudes are in good agreement with the experimental data. The obtained results offer better insights into the nature of colloidal force between charged particle stabilized nanoemulsions.

A new approach to study electron and positron scattering from acetylene

Studies on electron and positron scattering from acetylene are very important for their applications in the plasma and astronomical environments. In view of such importance, we have performed the cross section calculations for electron and positron scattering from acetylene molecule using the optical model potential method with an analytically obtained static potential. In the present study, the charge cloud of acetylene is represented through multi-center Gaussian wavefunctions and using the same, static potential seen by the projectile electron/positron is evaluated analytically with a new approach. A complex optical potential consisting of our analytical static potential with the appropriate exchange, polarization and absorption potentials has been obtained. Using this complex potential in the Schrodinger equation and utilizing partial wave analysis technique, the scattering phase shifts are evaluated for the electron and positron collisions with the acetylene molecule. Differential, integral, momentum transfer, absorption and total cross sections have been calculated for the incident projectile energies in the range 10−500 eV. The obtained results are compared with the previous available theoretical and experimental results, which show good agreement and thus demonstrate the applicability of our method.